28-11-2012, 06:27 PM
Weather Radar
[attachment=41593]
Radar - acronym for RADio Detection and Ranging
PS: Radar and lidar: major active remote sensing
Passive R.S. does not have ranging capability
Main components of a radar/lidar are:
Transmitter – “magnetron” which generates short pulses of electromagnetic energy (microwave)
Note: lidar uses shorter wavelength (UV, vis, NIR)
Antenna which emits and receives focused the energy into a narrow beam
Receiver which detects that portion of the transmitted energy that has been reflected (scattered) by objects with refractive characteristics different from air
Basic Operation Principles
Electromagnetic energy is transmitted into the atmosphere. Once reaching a target (cloud droplets, ice crystals, rain drops, snowflakes, aerosol particles, insects, birds, airplane, etc.), the energy is absorbed and scattered. A portion of backscattered energy is received and processed by a radar to display as an echo.
Two types of radar
Conventional radar – incoherent radar (1-2o beam width)
Detect only the intensity or the amplitude of
the electromagnetic energy – an incoherent sys
Doppler radar – coherent (phase) radar
Detect both the amplitude and phase of the
electromagnetic energy.
Important Radar Parameters
Detection capability of hydrometeor depends critically on radio frequency/wavelength.
In general, the smaller the size of the particles, the shorter the wavelength required to detect. e.g. the popular 10 cm (3 GHz or S-band) radar can detect rain drops but not cloud droplet which may be detected by 95 or 35 GHz radar.
Weather Radar and Rayleigh Scattering
the refractive terms depends upon , T and composition of the scatterer. For the meteorological range of temperatures and for common wavelengths
liquid water - ||2 ≈ 0.93
ice ||2 ≈ 0.21
Thus, an ice sphere has a radar cross-section only about 2/9 that of a water sphere of the same size.
For water-coated hailstone, k and varies strongly with water content, ranging from well below the values for ice to significantly higher than those for pure water. The later often displayed as a “bright band” in the radar screen, often associated with light precipitation in mix-phase clouds.
[attachment=41593]
Radar - acronym for RADio Detection and Ranging
PS: Radar and lidar: major active remote sensing
Passive R.S. does not have ranging capability
Main components of a radar/lidar are:
Transmitter – “magnetron” which generates short pulses of electromagnetic energy (microwave)
Note: lidar uses shorter wavelength (UV, vis, NIR)
Antenna which emits and receives focused the energy into a narrow beam
Receiver which detects that portion of the transmitted energy that has been reflected (scattered) by objects with refractive characteristics different from air
Basic Operation Principles
Electromagnetic energy is transmitted into the atmosphere. Once reaching a target (cloud droplets, ice crystals, rain drops, snowflakes, aerosol particles, insects, birds, airplane, etc.), the energy is absorbed and scattered. A portion of backscattered energy is received and processed by a radar to display as an echo.
Two types of radar
Conventional radar – incoherent radar (1-2o beam width)
Detect only the intensity or the amplitude of
the electromagnetic energy – an incoherent sys
Doppler radar – coherent (phase) radar
Detect both the amplitude and phase of the
electromagnetic energy.
Important Radar Parameters
Detection capability of hydrometeor depends critically on radio frequency/wavelength.
In general, the smaller the size of the particles, the shorter the wavelength required to detect. e.g. the popular 10 cm (3 GHz or S-band) radar can detect rain drops but not cloud droplet which may be detected by 95 or 35 GHz radar.
Weather Radar and Rayleigh Scattering
the refractive terms depends upon , T and composition of the scatterer. For the meteorological range of temperatures and for common wavelengths
liquid water - ||2 ≈ 0.93
ice ||2 ≈ 0.21
Thus, an ice sphere has a radar cross-section only about 2/9 that of a water sphere of the same size.
For water-coated hailstone, k and varies strongly with water content, ranging from well below the values for ice to significantly higher than those for pure water. The later often displayed as a “bright band” in the radar screen, often associated with light precipitation in mix-phase clouds.